Don't wrap system errors from function calls.

src/engine.rs

@@ -1939,7 +1939,7 @@ impl Engine {
                     Ok(_) => result,
                     Err(err) => match *err {
                         mut err @ EvalAltResult::ErrorRuntime(_, _) | mut err
-                            if err.catchable() =>
+                            if err.is_catchable() =>
                         {
                             let value = if let EvalAltResult::ErrorRuntime(ref x, _) = err {
                                 x.clone()

src/fn_call.rs

@@ -409,6 +409,9 @@ impl Engine {
                     )
                     .into()
                 }
+                // System errors are passed straight-through
+                err if err.is_system_exception() => Err(Box::new(err)),
+                // Other errors are wrapped in `ErrorInFunctionCall`
                 _ => EvalAltResult::ErrorInFunctionCall(
                     fn_def.name.to_string(),
                     err,

src/result.rs

@@ -270,10 +270,10 @@ impl<T: AsRef<str>> From<T> for Box<EvalAltResult> {
 
 impl EvalAltResult {
     /// Can this error be caught?
-    pub fn catchable(&self) -> bool {
+    pub fn is_catchable(&self) -> bool {
         match self {
             Self::ErrorSystem(_, _) => false,
-            Self::ErrorParsing(_, _) => false,
+            Self::ErrorParsing(_, _) => unreachable!(),
 
             Self::ErrorFunctionNotFound(_, _)
             | Self::ErrorInFunctionCall(_, _, _)
@@ -298,9 +298,28 @@ impl EvalAltResult {
             | Self::ErrorTooManyModules(_)
             | Self::ErrorStackOverflow(_)
             | Self::ErrorDataTooLarge(_, _, _, _)
-            | Self::ErrorTerminated(_)
-            | Self::LoopBreak(_, _)
-            | Self::Return(_, _) => false,
+            | Self::ErrorTerminated(_) => false,
+
+            Self::LoopBreak(_, _) | Self::Return(_, _) => unreachable!(),
+        }
+    }
+
+    /// Is this error a system exception?
+    pub fn is_system_exception(&self) -> bool {
+        match self {
+            Self::ErrorSystem(_, _) => true,
+            Self::ErrorParsing(_, _) => unreachable!(),
+
+            Self::ErrorTooManyOperations(_)
+            | Self::ErrorTooManyModules(_)
+            | Self::ErrorStackOverflow(_)
+            | Self::ErrorDataTooLarge(_, _, _, _) => true,
+
+            Self::ErrorTerminated(_) => true,
+
+            Self::LoopBreak(_, _) | Self::Return(_, _) => unreachable!(),
+
+            _ => false,
         }
     }
 

tests/operations.rs

@@ -72,7 +72,7 @@ fn test_max_operations_functions() -> Result<(), Box<EvalAltResult>> {
                     fn inc(x) { x + 1 }
                     let x = 0;
 
-                    while x < 30 {
+                    while x < 28 {
                         print(x);
                         x = inc(x);
                     }

tests/stack.rs

@@ -18,12 +18,15 @@ fn test_stack_overflow_fn_calls() -> Result<(), Box<EvalAltResult>> {
 
     #[cfg(not(feature = "unchecked"))]
     assert!(matches!(
-        *engine.eval::<()>(
-        r"
+        *engine
+            .eval::<()>(
+                r"
             fn foo(n) { if n == 0 { 0 } else { n + foo(n-1) } }
             foo(1000)
-    ").expect_err("should error"),
-        EvalAltResult::ErrorInFunctionCall(name, _, _) if name.starts_with("foo > foo > foo")
+    "
+            )
+            .expect_err("should error"),
+        EvalAltResult::ErrorStackOverflow(_)
     ));
 
     Ok(())